KR20040020909A - Apparatus and method for microwave determination of at least one physical parameter of a substance - Google Patents

Abstract

A method and an apparatus is described to measure at least one physical parameter of a substance such as moisture and salt content. This is done by transmitting a microwave beam through the material to be measured and detect only a reflection of a predetermined polarity of the transmitted waves. To accomplish this a polarizing plate is used so that only cross-polarized microwaves, which pass through the substance are detected and the co-polar reflections from surrounding structures are excluded. The object can either be moving as on a conveyer belt or in a rest position.

Description

A method and apparatus for measuring at least one physical variable of a substance using microwaves {APPARATUS AND METHOD FOR MICROWAVE DETERMINATION OF AT LEAST ONE PHYSICAL PARAMETER OF A SUBSTANCE}

It is well known that in the manufacture of various commodities such as wood, tobacco and food, the moisture content of the commodities plays a very important role before entering the final stage of the manufacturing process.

When measuring the moisture content using microwave radiation, the microwaves will react with the moisture molecules contained in the material being measured. Due to the dipole nature of the water molecules, the electric field of the microwaves causes the molecules to rotate and convert in response to the molecules to generate heat absorption of the incident energy. The moisture content of the material can be accurately measured by measuring the attenuation (energy loss) of the microwave according to the phase shift (speed loss) of the microwave. In general, this can be measured by converting the output signal into an electrical signal. Within certain materials the attenuation and phase shift can be used as a way of calculating the dielectric properties of the material. The dielectric properties of the material are expressed in complex permittivity. The complex permittivity is ε = ε '+ jε ", where ε' is the dielectric constant, which represents the extent to which the material can store electrical energy, and ε" is the loss factor, which represents the loss of the field energy in the material. Knowing ε 'and ε ", the water content and density of the material can be calculated from the formulas in the book.

In addition, other physical variables such as fat, protein and salt can also be measured, e.g. by using one or more frequencies and separating the energy absorption effect from water and the energy absorption effect from the presence of salt ions. The measurement of physical parameters is made possible because the frequency dependence of the loss mechanism of water and salt ions is different. Calibration can be performed by comparing the results obtained using traditional methods with repeated analysis using the device.

Microwave-based methods have not been able to measure physical variables such as fat, protein and salt in general, but only moisture content. For example, to date, there has been no device for measuring fat content using non-contact microwave technology. There has been a portable device for measuring fat content using microwaves. However, the device required firm contact with the material to be measured and substantially measured the moisture content. The device was precalibrated and the fat content was calculated from the measured moisture content.

Other systems and methods have been developed to measure the moisture content of materials. One was a handheld device, similar to the device mentioned above, called a "stripline" sensor. The device is placed on a material in such a manner that the stripline is closely adhered to the material. Then, when microwaves are generated and applied along the stripline, the attenuation is measured in the stripline. The attenuation or loss is converted to water content. This is a surface measurement method. In order to measure the overall moisture content of a large volume of material, it is necessary to make measurements at several places around the object. The average value is used as an index.

In another apparatus, the properties of the material can be inferred by placing the material between the transmitting and receiving antennas of the microwave delivery system and comparing the output signal from the material and the input source signal.

US Patent Publication 4,578,998 describes a microwave system using signals polarized in different directions. The two emitters measure across the planar material using polarized signals with two different polarities to avoid mutual interference between these two signals. The direction, ie polarity, of the wave is used to distinguish the radiator.

The problem with the U.S. Patent Publication No. 4,578,998 is that the measured signal includes not only attenuation passing through the material, but also reflected waves of microwaves reflected from unverified surrounding materials. This results in errors in the results.

A disadvantage of using portable contact devices is the surface measurement of large volumes of material. Due to the fact that measurements have to be made in various places around the material, it is time consuming to measure the material as a whole and the inconvenience of having to carry the device directly while carrying the device and connecting the sensor to the material. An error can occur because the device cannot be used in the same way all the time because it is directly measured by a person.

The present invention relates to a method and apparatus for measuring at least one physical parameter of an object by scanning microwaves towards the object and analyzing the reflected and microwaves scanned in the same and opposite polarized waves.

Figure 1 shows a flowchart of one embodiment that can be used as a method for measuring moisture content in the present invention.

2A and 2B illustrate an embodiment of an apparatus in which the method of the present invention may be used.

3 is a diagram of a second embodiment that may be used with the present invention to measure moisture content. This embodiment also measures the depth of the object or material being measured and thus also the density.

4 is a graph showing a sample of an electrical response to the presence of an object or material in the scanning beam used to calculate the density and moisture of the object to be measured.

5 is an embodiment of the polarization device.

6 is a graph of experimental results using the apparatus.

It is an object of the present invention to provide a method and apparatus for measuring at least one physical parameter of a substance, such as the moisture and fat content of a large material, as described above. This is accomplished by using the polarity, or polarization, of the microwave to create a path through the sample, where only the reflected wave is polarized through the material to be measured and polarized in a predetermined direction among the transmitted waves. This has the advantage that only the signal passing through the material is measured. This is accomplished by using a polarizing plate such that counter-polarized microwaves passing through the material are detected and the same-polarized reflected wave reflected from the surrounding constituent material is excluded. Thus, this increases the accuracy and sensitivity of the measurement. Therefore, only the microwaves reflected by the polarization plate after passing through the material to be measured are received. If the system has been installed to detect anti-polarized reflected waves, it is certain that the microwave to be measured has already passed the object twice before being measured. If the system is installed to detect co-polarized echoes, it is possible to measure the distance from the slit of the receiving antenna to the surface of the material, which is compared to the co-polarized echoes in the absence of any measurement material. May be related to depth.

A first aspect of the invention relates to an apparatus for measuring at least one physical variable of an object by scanning a microwave towards the object to be measured and analyzing the reflected wave, the apparatus comprising the following configuration.

A source device for generating time-dependent electrical signals,

A scanning device disposed proximate to the object, for converting the time dependent electrical signal into a microwave and for scanning the microwave into the object,

A polarization device disposed adjacent to the object and located opposite the scanning device, for rotating at least a part of the polarization direction of the scanned wave and for reflecting the scanning wave having a predetermined polarization direction,

A receiving device positioned opposite the object together with the polarizing device, for receiving the reflected microwaves polarized in a predetermined direction and converting the reflected waves into an electrical signal, and

A computer system for calculating at least one physical variable of the object using the electrical signal.

In addition, it is preferable to be provided with an electronic control device for controlling the source device. The polarization device may be configured as a flat plate including a plurality of parallel metal lines in a horizontal flat plate of the polarizing plate to rotate at least a portion of the scanning wave. The metal wires may be supported by an antireflective material such as a plastic material. The lower layer of the polarizing plate is a reflective material such as a metal plate. When the microwave is scanned on the polarizing plate, part of the microwave hits the metal wire rotating the polarization direction, and part passes through the support until it is reflected from the lower plate through the metal wire. The underlayer reflects the microwaves by the law of reflection, where a portion of the reflected microwaves strikes the metal wire that rotates the polarization direction. If the thickness of the polarizing plate, that is, the spacing between the metal wire and the lower layer plate, is properly adjusted, the "second" polarization direction and the "first" polarization direction may be the same. Preferably, the interval is (1/4) λ or generally (1/4 + n) λ, where λ is the wavelength of the microwave and n is an integer. In general, there is air between the metal wire and the lower plate. However, when there is any material between the metal wire and the reflector, the thickness ratio will be different and depend on the dielectric properties of the material. The microwaves of which the polarization direction is rotated are received by the receiving device which converts the microwaves into electric signals. The polarization direction of the received microwave can be rotated 90 degrees with respect to the scanned microwave, and the microwave can be linearly or circularly polarized. For example, the receiving device may be an antenna or a dipole antenna.

The frequency of the time-dependent electric source signal depends on whether it measures several variables, such as water and salinity, or one variable, such as water. This is because the properties of the water and salt molecules and their resonant frequencies are different. In one embodiment of this, the time-dependent electrical signal has a frequency that is sequentially repeated. That is, the frequency for the first moisture measurement and the other for the salinity measurement. Thus, the time dependent electromagnetic field has at least one frequency.

In order to measure at least one physical variable of the object to be measured, the physical variable here can be the moisture content and / or density of the object, and it is also useful to use a common channel. In one embodiment, the device is provided comprising a coupler for distributing the electrical signal to the scanning device and the receiving device which can be used as a scanning antenna. Here, a part of the electrical signal directed to the receiving device passes through a common channel, and this signal is used as a reference signal. Preferably, half of the source signal passes through a common channel and the other half is distributed to the scanning antenna.

The measurement of the object to be measured may be performed in a stationary state or in a conveying state such as a conveyor belt. In general, the scan and receive antennas are in close proximity to a suitable location above the object, with the radiation pattern directed directly at the object. For attenuation measurements, the antennas are installed to have a perpendicular polarization direction with respect to each other.

It is also important to measure the thickness of the material in order to measure the dielectric constant of the material. One way to measure this is to install another second receive antenna in close proximity to the scanning antenna above the polarizer and the object. Thus, the same-polarized signal measures the difference in distance between when there is no material and when there is material. Preferably, in this case, the polarization direction of the received microwave becomes the same as the scanning microwave. Ultrasonic waves can also be used for the same purpose.

Another aspect of the invention provides a method of measuring at least one physical variable of an object by scanning microwave towards the object and measuring the reflected wave, the method comprising the following steps.

Generating a first time dependent electrical signal and converting at least a portion of the first electrical signal into microwaves,

Scanning the microwave towards the object,

Reflecting the scanning microwaves by means of a polarizing device which is arranged in proximity to the object and located opposite the scanning device, in which at least some polarization direction of the reflected microwaves is rotated,

Receiving, at a receiving device opposite to the object, a portion of the microwave reflected from the polarizing device in which the polarization direction is rotated, and converting a portion of the received scanning wave into a second electrical signal,

Analyzing the second signal and measuring at least one physical variable.

In one embodiment, the time dependent electrical signal output from the source is divided into two, partly transmitted over a common channel and partly transmitted from a polarization device to a receiving means, and eventually the two signals are merged again. do. For example, if there is no material on the polarizer, the combined signal is used as a reference signal having a reference level and a reference phase. When an object is in the polarization device, the distortion of the reference phase and the reference level is used to measure the complex dielectric constant of the object in any form. The reference phase or frequency shift is used to calculate the dielectric constant [epsilon] 'of the object and the shift of the reference level can be used to measure the loss factor [epsilon]. Other variables that are important when calculating [epsilon] and [epsilon] are: The thickness of the material through which microwaves travel. This variable can be measured, for example, by using a second receiving means opposite the object with the polarization device. Preferably, the second receiving means is adapted to detect microwaves in a polarization direction such as scanned microwaves. Thus, a portion of the microwave reflected from the object is measured and compared with the reference signal. For example, a signal in the absence of an object and a phase shift from the reference signal are used to measure the height of the object. If the distance between the slit and the polarizing plate and the angle radiated from the scanning horn are known, the effective measuring area can be measured. Together with the thickness, the volume is calculated.

The scanned microwave is a linearly polarized wave, and the polarized portion of the reflected wave detected by the receiving means is preferably polarized by 90 degrees with respect to the scanned microwave.

This proves that only a part of the scanning wave passing through the object is detected, where the polarization device is located below the object, so that the microwave in the polarization direction must pass through the object. One method of measuring the phase change and attenuation change in the material is to use a common channel. In the absence of material, the use of adjustable attenuators and phase shifters in the common channel will result in the sum of the reflected signal of the polarization device and the signal in the common channel being zero. For example, if the fibrous tissue in the material is mainly in one direction, for example in the vertical direction of the scanning horn, it is possible to use circular polarization rather than linear polarization of the microwave.

In addition, the moisture content can be used to measure the fat content of an object such as a fish. Since buoyancy is known and constant, the relationship between fat and water in the body of the fish is established by an experimental formula. This can also be obtained from the recorded data.

In the following, particularly preferred embodiments of the present invention will be described in detail with reference to the drawings.

Figure 1 shows a flowchart of one embodiment that can be used as a method for measuring moisture content in the present invention. The device comprises a microwave radiation source 1 visible to the left of the coupler 2. In a preferred embodiment, the microwave radiation source 1 is a swept source that continuously scans microwaves having a frequency that varies linearly with time, preferably over a certain frequency bandwidth. The source (or sources) may be prepared to scan one or more center frequencies. A sweeping source that continuously changes the frequency, ie a sweep source, receives a signal from the switch 15 before sending the signal to the coupler 2. The switch 15 determines which center frequency it will have.

The signal from the sweep source 1 is amplified once at an appropriate level and distributed at the coupler 2, with some signals being transmitted to the receiving device 7 via a common channel while the remaining signals are transmitted to the measuring channel. Transmitted to the scanning antenna 4. Preferably, the signals transmitted in the two different directions are the same, and each signal is exactly 50% of the original signal.

The sample to be measured can be replaced by a continuous flow of large objects without departing from the principles of the present invention. The reason for this is to be noted that the following description of the device will only describe simple samples.

The microwave will be detected in the sample by means such as scanning antenna 4. Similarly, planar antennas can be used for the same purpose.

The source signal 10a is a microwave signal of very high frequency. The microwave signal is a frequency modulated signal by linearly sweeping, ie, sweeping, the source oscillator from a slightly lower frequency to a slightly higher frequency than the center frequency on a predetermined bandwidth. The type of sample determines the preferred center frequency of the source signal, and the number of frequencies used depends on the number of physical variables to be measured, such as moisture, salinity or protein.

The source signal 10a passes through the sample 14 and hits the polarization device 5 and is reflected back. As the source signal 10a passes through the sample, it is attenuated and slowed down. The degree of attenuation is mainly determined by the loss factor ε "of the material of the sample 14 through which the source signal passes. The extent to which the source signal is slowed is mainly determined by the dielectric constant ε 'of the material 14. Is determined.

When the source signal 10a strikes the polarization device 5, the polarization device 5 changes the polarization direction of the signal by the signal of the reception antenna 6. The scanning antenna 4 and the receiving antenna 6 are exactly the same except that the polarization directions are orthogonal to each other. This means that no reflections from the sample, the conveyor belt or the conveyor belt structure or any surrounding object and any direction radiating from the scanning antenna 4 are detected at the receiving device 7, since these signals are This is because it has a polarization direction that is not suitable for incidence to the antenna 6. If the system is calibrated, the receiving device 7 theoretically detects only the electrical change of the measurement signal due to the sample 14 in the system.

The sample 14 exhibits additional phase shift and attenuation in the measurement channel. In a preferred embodiment, there is only one receiving antenna, but there may be more than one receiving antenna.

In one embodiment, a frequency mixer is used in both the common and measurement channels to measure the phase difference. In another embodiment, the reference signal 8a is transmitted to the attenuator and phase shifter 3. During calibration, the attenuator and phase shifter 3 are set such that the common channel responds to the electrical characteristics of the measurement channel in the absence of sample 14 or in the case of known samples.

At the receiver input, the receiving device 7 adds the reference signal 8b and the measurement signal 10b in anti-phase. Insertion phase shifts and attenuations in the common channel generating zero signals at the receiving device are recorded. The recorded phase shift and the attenuation are sent to the processor where the calculation of physical parameters such as moisture is made.

In an apparatus in which at least one frequency is used, the method is the same as above and the switch 15 switches to another frequency.

One embodiment has been described above. In general, there are four main methods for measuring.

1. The simplest embodiment will be the use of a sweep oscillator 1 with both an electrically controllable (programmable) phase shifter and an attenuator 3 on the common channel. In this embodiment, the phase shifter and attenuator 3 controlled by the receiving device is configured such that the added signals at the input of the receiving device at the calibration frequency are " zero " Until it is output. When the sample 14 is present, a record of the attenuation and the change in phase shift is sent to the processor.

2. The source 1 is swept, i.e. not sweeped but frequency adjustable, and the common channel comprises only an electrically controllable attenuator 3. In this case the oscillator frequency and the attenuator 3 are adjusted to output a zero signal at the receiving device 7. Records of changes in frequency and attenuation are passed to the processor.

3. A sweep, or swept frequency source 3, is used to generate the frequency response to be output at the receiving device, as shown in FIG. The receiving electronic device is required to be able to record a change in the form of the frequency response which is more complicated and a sign of the phase change and attenuation change due to the material being measured. In this case, the programmable phase shifter and attenuator of the common channel are not necessary because more complex electronics provide the necessary phase shift and attenuation information. However, the hand-adjusted attenuator and phase shifter 17 of FIG. 3 are still present to calibrate the system to realize the zero input signal or the exact opposite phase signal of FIG. 4 at a particular frequency when no sample is present. Will be.

4. The source 3 is not sweeping, ie unswept, and the attenuation change and the phase shift change due to the insertion of a sample, i.e. the magnitude of the attenuation and the magnitude of the phase, separate anti-polarization reception Measured directly through the channel. In the attenuation magnitude channel, a rectifying diode measures the attenuation in the sample. Used to provide a signal level. In the phase channel, a dual balanced frequency mixer is used to provide an I.F. (d.c.) Signal level that measures the phase change by the sample.

2A and 2B illustrate an embodiment of the present invention, showing a very simple device version. The microwave source 1 may be a sweep source and generates a time dependent electrical signal. Some of the signal is distributed in the coupler 2, some of which is used as the reference signal 9 while the other is transmitted to the scanning antenna 4, some of which pass through the object 14. Is reflected from the polarization device 5. This is called the measurement signal 11.

3 is a diagram of a second embodiment of an apparatus that may be used with the present invention. This device measures the moisture and salinity of the sample (tobacco) similar to the device of FIG. 2. The sample may be stationary or being transferred on a conveyor belt.

The device uses two frequencies because it measures two different physical variables of moisture and salt content. Thus, the switch 15 is switched between 8 GHz and 12 GHz after receiving a signal from the receiving device 7. Other frequencies show the same result.

The device comprises a micro spinning source 1. The sweep source 1 receives a signal from the switch 15 before sending a signal to the coupler 2. The signal from the sweep source 1 is amplified to an appropriate level and distributed in the coupler 2, and partly transmitted to the receiving device 7 via the common channel as a reference signal 8a, while the remaining signal Is transmitted to the scanning antenna 4 as a measurement signal 10a. The signals going in two different directions are ideally identical, with each signal being exactly 50% of the original signal.

The microwave is directed directly to the sample and scanned from the scanning antenna 4. The source 1 is a microwave oscillator of a very high frequency and the frequency is changed linearly with time in a repeating manner in a predetermined band region.

A portion of the scan signal 11 passes through the sample 14 and hits the polarization device and is reflected back. The other part of the scan signal 25 is the signal reflected to the sample. The former is received at the same-polarized receive antenna 19 and used to measure the thickness of the sample 14 by detecting the phase shift of the first reflection. The signal hitting the polarization device through the sample 14 is received by the transversely polarized reception antenna 6 after the polarization direction is changed and reflected.

The reference signal 8a is transmitted to a manually adjusted attenuator and phase shifter 17 and then to a programmable / variable attenuator and phase shifter 18. If the device is set up to zero the summation signal at a particular frequency during a frequency sweep when there is no workpiece, the manually tuned attenuator and phase shifter 17 are used to calibrate the signal. When there is a sample, the attenuation and phase shift of the microwave in the measurement channel is increased and the signal 10b is weakened when input to the antenna 6. Then, in order to adjust the programmable / variable attenuator and phase shifter 18 so that the sum of the signals is again zero, the receiving device 7 transmits a signal. The adjustment amount is recorded as a measurement of the attenuation and phase of the sample.

An infrared thermometer 20 measures the temperature of the sample 14 and transmits this signal to the receiving device so that the measurement of the complex dielectric constant can be corrected with temperature.

The receiving device 7 adds the reference signal 8b and the measurement signal 10b to be in opposite phase. When the phase shift and attenuation 18 is correctly adjusted, if a zero signal is detected, this means that the attenuation at 8b is the same as the attenuation at 10b. Then, the phase shift and attenuation in the common channel are recorded. The detected phase shift and attenuation is sent to a processor. The processor calculates and converts the values into meaningful information.

4 graphically illustrates an example of an electrical signal from a receiving device 7 used for calculating ε 'and ε "of a sample. The x-axis shows the frequency sweep of the source and the y-axis shows the strength of the signal. First, when there is no sample, the system shows a response of 26. If there is a sample, the attenuation in the material increases attenuation of the scanning microwave and a phase change occurs. Since the sum of the measurement signal and the reference signal changes if a sample is present, this is represented by the response curve 27. The difference in the horizontal direction represents the phase change and the difference in the horizontal direction is attenuation due to the sample. And these variables are used to calculate ε 'and ε "according to the formulas in the book.

Both the wet weight and the density measurement are based on recorded data that depends on the object, such as tobacco, wood or corn. Each of these objects has a relationship between their own phase shift and attenuation and substantial moisture content and density. Rather than using a formula, one can choose to collect data from the device and match the actual values of moisture and density.

In FIG. 4, curve 26 shows the signal measured when no sample is measured as in FIG. 2A. In this case, the measured signal is the same as the reference signal but has a different polarization direction. Therefore, the combination of the reference signal and the measurement signal becomes zero at a specific frequency. The reference value is zero when there is no moisture.

As the signal passes through the sample with moisture, measurement curve 27 appears. In this case, the sample is reduced or attenuated by 50% of the signal. Since the reference signal has not changed, the sum of the reference signal and the measurement signal is changed by 50% in the vertical direction. The vertical direction is the damping axis. If the sample is pure water, it absorbs all of the microwaves and attenuates the measurement signal to zero. Only the reference signal is received and appears as a straight line at the attenuation level of the reference signal.

In addition, the curve 27 shows the phase shift of the microwave during the frequency sweep, and it can be seen that the lowest point of the curve signal has moved left from f0 to f1. The phase shift is used to calculate the density of the sample as mentioned above.

By calculating the density using the complex dielectric constant, if the wet weight m _wet and the dry weight m _dry and the volume V of the material are known, the density calculation formula ρ = (m _wet + m _dry ) / V can be calculated. As shown in FIG. 3, the volume can be calculated using a co-polarized reception antenna 19 for measuring the thickness of the sample 14 which is periodically updated. If the object is being conveyed at a constant speed on the conveyor belt, the object can be divided into several parts having a certain length and a different thickness.

FIG. 5 shows an embodiment of the polarization device, wherein the polarization device is configured by placing metal wires 28 parallel to the horizontal plane of the polarization plate to rotate at least a portion of the scanning wave. These metal wires may be supported by an antireflective material 29, such as a plastic material. The lower layer of the polarizing plate may be made of a reflective material such as the metal plate 30. When the microwaves are irradiated to the polarizer, some of them are aligned with the metal wires, and the polarization direction is rotated, and some of them pass through the supporting object until they pass through the metal wires and are reflected from the lower plate 30.

Position the side of the polarization device in parallel to the line between the scanning antenna 4 and the receiving antenna 6, and make the incident from the scanning antenna 4 by equalizing two 45 degrees of 31 and 32. Both the microwave and the microwave reflected from the lower plate 30 hit the metal wire 28 in a path outside the non-reflective material 29 so that the polarization direction can be rotated 90 degrees.

The present invention will be further explained by the following experimental example, which is not intended to limit the present invention in any sense.

Experimental Example

The following example is based on the results of the experiment, in which nine tea leaves were used as samples, each of the tea leaves had a water content of about 100 g, each having a different 5% to 20% moisture content. Two sweep frequencies were used, one about 8 GHz and the other about 12 GHz. Attenuation was measured in the sample but no phase change. In this experiment a linear relationship between attenuation and the actual moisture content of the sample is shown as shown in FIG. 6. The correlation coefficient was 0.9914 at 8 GHz and 0.9789 at 12 GHz. The correlation coefficient is 0 to 1, indicating how well the data point lies on the alignment line.

Claims (25)

An apparatus for measuring at least one physical parameter of an object by scanning a microwave towards the object and analyzing the reflected wave, Source device for generating time-dependent electrical signals, A scanning device disposed proximate to the object, for converting the time dependent electrical signal into a microwave and for scanning the microwave into the object, A polarization device disposed adjacent to the object and positioned opposite the scanning device, rotating at least a portion of the polarization direction of the scanning wave, and reflecting the scanning wave having a predetermined polarization direction; A receiving device positioned opposite the object together with the polarization device, for receiving reflected microwaves having a predetermined polarization direction, and for converting the reflected waves into electrical signals; And a computer system for calculating at least one physical variable of the object using the electrical signal. The method of claim 1, And a control electronic device for controlling the source. The method according to claim 1 or 2, And said polarization device comprises a flat plate comprising a plurality of parallel metal wires in a horizontal flat plate for rotating at least a portion of said scanning wave. The method according to any one of the preceding claims, The thickness of the polarization device is a measuring device using a microwave, characterized in that 1/4 of the wavelength of the microwave. The method according to any one of the preceding claims, The apparatus further comprises a coupler for distributing the electrical signal to the scanning device and the receiving device, A portion of the electrical signal transmitted to the receiving device passes through a common channel, the signal is a microwave measurement device, characterized in that used as a reference signal. The method according to any one of the preceding claims, And measuring the object while the object is being measured. The method according to any one of the preceding claims, And the receiving device and the scanning device are perpendicular to each other and the receiving device corresponds directly to the material. The method according to any one of the preceding claims, At least one physical variable is the density or water content of the object or both the density and the water content of the object. The method according to any one of the preceding claims, The receiving device is a measuring device using a microwave, characterized in that the antenna. The method according to any one of the preceding claims, The receiving device is a measuring device using a microwave, characterized in that the diode. The method according to any one of the preceding claims, And the scanned microwaves are linearly polarized. The method of claim 1, wherein The scanning microwave is a measurement device using a microwave, characterized in that the circularly polarized. The method according to any one of the preceding claims, And a second receiving device disposed above the polarization device and the object and configured to receive at least a portion of the reflected microwaves. The method according to any one of the preceding claims, And the polarization direction of the received microwave is the same as that of the scanned microwave. A method of scanning at least one physical variable of an object by scanning a microwave towards the object and measuring the reflected wave, Generating a first time dependent electrical signal and converting at least a portion of the first electrical signal into polarized microwaves, Scanning the polarized microwaves towards the object, Reflecting the scanned microwaves in a polarization device disposed in proximity to the object and located opposite the scanning device, in which at least a partial polarization direction of the reflected microwaves is rotated, Receiving, at a receiving device opposite the object, a portion in which the polarization direction is rotated among the reflected microwaves, and converting a portion of the received scanning wave into a second electrical signal; and Analyzing the second signal and measuring at least one physical variable. The method of claim 15, And a part of said first electrical signal is transmitted to said receiving means through a common channel and used as a reference signal. The method according to claim 15 or 16, And the rotation of the at least part of the scanned microwave in the polarization direction is 90 degrees. The method according to any one of claims 15 to 17, The sum of the second electrical signal and the reference signal is used to measure at least one physical variable. The method according to any one of claims 15 to 18, The second electrical signal is used to measure at least one physical variable. The method according to any one of claims 15 to 19, Receiving the at least a portion of the reflected wave polarized in the predetermined direction, wherein the received microwave is converted into an electrical signal and uses a phase shift of the electrical signal relative to a reference signal to measure the height of the object And a second receiving means positioned opposite to the object. The method according to any one of claims 15 to 20, Wherein said attenuation level and said phase shift of said signal are used to calculate the dielectric constant and loss factor of said object. The method according to any one of claims 15 to 21, The dielectric constant and the loss factor of the object are used to calculate the density of the object. The method according to any one of claims 15 to 22, The dielectric constant and the loss factor of the object are used to calculate the water content of the object. The method according to any one of claims 15 to 23, And said volume, said density and said water content of said object are used to measure the weight of the dry mass of said object. The method according to any one of claims 15 to 24, And measuring at least one physical variable of the object based on recorded data.